The present invention relates to a communication terminal apparatus, base station apparatus, and radio communication method for use in high-speed data communication.
One multiple access method in a digital radio communication system is CDMA (Code Division Multiple Access). In a standard established by 3GPP (3rd Generation Partnership Project), a standards body related to mobile radio communication systems, this CDMA method is used and a Downlink Shared Channel (DSCH) used for high-speed data communication in a downlink (a channel from a base station to a communication terminal) is stipulated as one channel shared by a plurality of communication terminals.
As this DSCH is used by being assigned to each communication terminal on a specified transmission unit basis (for example, on a frame-by-frame basis), its use is anticipated in downlink high-speed packet transmission, etc.
In high-speed packet transmission using a DSCH, a base station generally performs DSCH assignment to each communication terminal according to information indicating communication quality (such as the received SIR at each communication terminal, for example), information indicating the modulation/demodulation method, and so forth, in the event of DSCH assignment requests from communication terminals.
Also, since the above-described DSCH is assigned to communication terminals on a per-predetermined-transmission-unit basis, in high-speed packet transmission using a DSCH there are many cases in which packets to a particular communication terminal are transmitted dispersed time-wise.
A downlink channel for high-speed data communication shared by a plurality of communication terminals, as with a DSCH, is hereinafter referred to as a xe2x80x9cshared channelxe2x80x9d, and information required during assignment of this shared channel or during communication using a shared channel is hereinafter referred to as xe2x80x9cshared channel informationxe2x80x9d.
However, in a conventional radio communication method, each communication terminal constantly transmits shared channel information to a base station regardless of whether or not there is a DSCH assignment request. Also, each communication terminal constantly transmits shared channel information to a base station even when the DSCH has not been assigned to that terminal.
When communication terminals constantly transmit shared channel information to a base station in this way, there are problems in that communication terminal power consumption increases, and in addition, interference imposed by a signal containing shared channel information on other signals increases in uplinks (channels from communication terminals to a base station). Moreover, the increase in interference results in a problem of reduced system capacity.
It is an object of the present invention to provide a communication terminal apparatus, base station apparatus, and radio communication method that enable communication terminal apparatus power consumption to be reduced, and also enable interference in uplinks to be reduced.
The present inventors arrived at the present invention by noting that there is a difference in the degree of frequency and content of shared channel information needed by a base station when a DSCH is either assigned or not.
That is to say, the present inventors arrived at the present invention by noting that a communication terminal to which a DSCH is assigned needs to constantly transmit shared channel information so that a base station can keep up with changes in propagation path conditions and changes in the modulation/demodulation method in real time and transmit the DSCH signal efficiently, whereas a communication terminal to which a DSCH is not assigned needs to only transmit shared channel information at the minimum degree of frequency necessary for DSCH assignment to be performed by the base station, and finding that a communication terminal to which the DSCH is not assigned can reduce the frequency of transmission of shared channel information.
Furthermore, the present inventors arrived at the present invention by noting that a communication terminal to which a DSCH is assigned needs to transmit all shared channel information including the modulation/demodulation method, and so forth, whereas a communication terminal to which a DSCH is not assigned needs to transmit, of shared channel information, only information necessary for DSCH assignment to be performed by the base station (information indicating communication quality, etc.), and finding that a communication terminal to which the DSCH is not assigned can reduce the amount of information in shared channel information.
Thus, in order to achieve the above object, the present invention changes as appropriate the degree of frequency of transmission and amount of information of shared channel information according to necessity at a base station, and transmits only the necessary amount of shared channel information according to the communication conditions between a communication terminal and a base station, thereby enabling the communication terminal power consumption to be reduced, and also enabling interference in uplinks to be reduced.